Unique vascular morphology of the fourth aortic arches: possible implications for pathogenesis of type-B aortic arch interruption and anomalous rightsubclavian artery

Objective: Neural crest-derived cells were previously shown to participate in vessel wall formation of the great thoracic arteries, and their contribu tion was proposed to affect morphology and physiology of these vessels in t he chick. The present investigation was undertaken to examine vascular diff erentiation and morphogenesis of the neural crest-derived aortic arches in mammals. Methods: Using immunohistochemical markers for smooth muscle cell differentiation and a neurofilament marker, we examined morphogenesis of th e great arteries in mice, ranging from embryonic day 11.5 to the adult. Res ults: We observed that in the 4th aortic arch arteries early media formatio n differed from the other arteries, in that they almost completely lacked ( or showed decreased) actin expression in certain areas. This discontinuity in actin expression persisted throughout much of foetal development, in the form of circular segments of cells displaying decreased staining for smoot h muscle markers, both at the left and right side of the arterial tree. In adult mice, the 4th arch artery derivatives, segment B of the aortic arch a nd the proximal right subclavian artery, were observed to differ from adjoi ning vessels in their smooth muscle and elastic composition. Staining for n eurofilaments revealed close association of the developing segments with ap parent sensory afferent vascular innervation. Conclusion: The unique areas of the 4th arch artery identified here reflect the basic segmental patterni ng of the early embryonic pharyngeal arches. These segments correlate with sites that are predisposed to interruption or severe hypoplasia, and may th us reveal part of the aetiology of type-B aortic arch interruptions and art eria lusoria. (C) 1999 Elsevier Science B.V. All rights reserved.